Underwater molten salt heat storage boiler

ABSTRACT

1. An underwater vehicle including apparatus for generating steam for propelling same, comprising; A. A CLOSED THIN WALL CONTAINER HAVING A VOID SPACE AT ITS UPPER END, B. A MELTABLE SALT MIXTURE FILLING SAID CONTAINER BELOW SAID SPACE, SAID MIXTURE HAVING SUBSTANTIALLY ZERO COEFFICIENT OF EXPANSION AT ITS SOLIDIFYING TEMPERATURE, THE SOLIDIFYING TEMPERATURE BEING IN EXCESS OF 212* F, c. the outside of said container being in contact with and subjected to water at ambient pressure, D. MEANS FOR PRESSURIZING SAID SPACE TO AMBIENT WATER PRESSURE WHEREBY THE SALT MIXTURE, WHEN MELTED, SUBJECTS THE INSIDE OF SAID CONTAINER TO AMBIENT WATER PRESSURE, E. A STEAM GENERATING COIL DISPOSED WITHIN SAID SALT MIXTURE HAVING A WATER INLET AT ITS LOWER END AND A STEAM OUTLET AT ITS UPPER END ADAPTED TO EXTRACT HEAT FROM THE SALT MIXTURE AND CAUSE IT TO SOLIDIFY, FIRST AT THE BOTTOM OF THE CONTAINER, AND THEREAFTER IN SUCCEEDING LAYERS THEREABOVE, AND F. A SOURCE OF SUPERHEATED STEAM FOR MELTING SAID SALT MIXTURE DISPOSED AT THE SURFACE OF THE WATER AND MEANS FOR CONNECTING SAID COIL TO SAME.

United States Patent 1191 Karig et al. 1 Mar. 27, 1973 [54] UNDERWATER MOLTEN SALT HEAT EXEMPLARY CLAIM STORAGE BOILER 1. An underwater vehicle including apparatus for [75] lnventors: Horace Edmund Karig, Pasadena; generating steam for propelling same, comprising;

Gerrit DeVries, Altadena, both of a. a closed thin wall container having a void space Calif. at its upper end, b. a meltable salt mixture filling said container [73] Asslgnee. The Umte: bStagles sof Atmericta as below Said Space, said mixture having Substam rNepresente y e ecre ary 0 e tially zero coefficient of expansion at its solidifying temperature, the solidifying temperature 22 Filed: 061. 21, 1965 being in excess of F,

1 c. the outside of said container being in contact with [21 1 Appl- 5002389 and subjected to water at ambient pressure,

d. means for pressurizing said space to ambient 52 us. (:1 ..114/16 G, 122/32 Water W whereby the Salt mixture, when 51 Int. c1..'.... 63 19/00, B63g 21/06, B63g 21/08 meItFd, sublects the mslde 5 Contamer t [58] Field Of Search ..114/20-2s, 16; when Water P e 7 122/332 33; 23/302 303 e. a steam generating C011 disposed wlthm said salt mixture having a water inlet at its lower end and a 56 R f mes Citedsteam outlet at its upper end adapted to extract 1 e ere heat from the salt mixture and cause it to solidify, UNITED STATES PATENTS first at the bottom of the container, and thereafter 1 987 182 1/1935 Delan et al. 122/33 in succeeding layers thereabm'e and 2:791:204 5/1957 Andrus ..122/33 3 slperheated Steam metmg 9 3 109 401 11/1963 Karig ..114/20 Salt mlxture dslmed the water g and means for oonnectmg said coil to same. Primary Examiner-Benjamin A. Borchelt 4 Claims 3 Drawing Figures Assistant Examiner-Thomas H. Webb Att0rney-R. S. Sciascia and E. F. Johnston PATEIUEDHARZHHTS 3 a m s m m m m M K W W 6 E I F 8 4 A VE. M L O A l 6 m C. 3 E 7 Lu W 1 6 Q J M 2 V R R 8 r: v V M 0M M 2 r; n u m m n T m a m nm; E C 4 2 a i u= o 0. u z 0. K L 0 2 MN ATTORNEY.

UNDERWATER MOLTEN SALT HEAT STORAGE BOILER The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to underwater vehicle propulsion systems and more particularly to improvements in steam boilers for use with the same.

In the art of anti-submarine warfare a recent concept contemplates the use of an unmanned underwater vehicle which is self-propelled at considerable depth beneath a moving surface ship and which is provided with suitable sonar apparatus for detecting the location of enemy submarines. The information received by the vehicle is telemetered to the surface ship which may then launch a suitable missile, such as ASROC, for destroying the submarine. It is highly desirable that the underwater vehicle have as long an operating range as possible to thus minimize the intervals at which it is brought to the surface, under command from the surface ship, for recharging its energy source.

The underwater drone vehicle is substantially spherical in shape and is slightly positively buoyant, being maintained at desired depth by its forward motion and suitable hydrodynamic surfaces. Conventional rudders are provided, controlled by the surface ship, for maneuvering it along a course substantially directly below the course of the surface ship. Except for certain sonar, telemetering, and propulsion components, the spherical hull is flooded with sea water at ambient pressure thus permitting the use of a thin wall unstressed hull.

Various energy sources for propelling the vehicle are conceivable, rechargeable batteries probably being one of the most simple forms. Batteries, however, suffer the disadvantages of low energy density, long recharging time and limited cycles of recharging. Replenished sources of energy, such as fuels or propellants, while having higher energy densities, have certain disadvantages including difficulties of control of combustion rates, heavy stressed combustion chambers and the like, buoyancy changes due to depletion of fuel and generation of noise by exhaust gases.

One of the objects of this invention is to provide an energy source for use in a self-propelled underwater vehicle which may be quickly and readily recharged at intervals by an available heat source on a surface ship.

Another object is to pressure balance the energy source to ambient water pressure whereby the use of heavy chambers and the like is obviated.

A further object is to provide a heat source, in the form of a heat sink, of meltable salts having high heat content per unit of weight and volume.

A still further object is to provide a heat sink in the form of a specific mixture of salts which have substantially zero coefficient of expansion when they change from liquid to solid state.

Still further objects, advantages and salient features will become more apparent from the description to follow, the appended claims, and the accompanying drawing, in which:

FIG. 1 illustrates an environment of the invention;

FIG. 2 is a schematic of the essential components of a steam power plant system, and

FIG. 3 is a cross section of a steam boiler, illustrated schematically in FIG. 2.

Referring now to the drawing, and first to FIG. I, an exemplary environment of the invention is illustrated as contained within an underwater vehicle 10 which is self-propelled and follows the course of surface ship 12 at a desired depth of submergence and which detects the presence of a submarine 14, telemetering such information to the surface ship, all as previously referred to.

Referring now to FIG. 2, vehicle 10 contains a boiler 16 comprising a container 18 and a steam generating coil 20 within the container, the coil being submerged in a salt mixture 22 to be hereinafter described in more detail.

In operation, feed water is delivered to the coil by a pump 24, producing steam, which is delivered to a steam engine 26, thence to a condenser 28 and back to the pump for recirculation to the boiler. The engine is connected to a suitable propeller or pump-jet rotor 30 for propelling the vehicle. A valve 32, under suitable control, may be provided to control the speed and power delivered by the engine and a by-pass or relief valve 34 may be provided to control the boiler steam generation rate and pressure.

Referring now to FIG. 3, container 18 may be of any suitable shape, such as cylindrical, which will fit within the generally spherical vehicle 10. Container 18 is completely surrounded by porous heat insulation 36, the outer surface of which is completely covered by a flexible bag 38, such as rubber, which prevents sea water from entering the insulation and destroying its insulating characteristics. To simplify the disclosure, coil 20 is illustrated in the form of a single cylindrical helix, however, in actual practice the coil 20 would preferably be more uniformly distributed throughout the mass of the salt bed 22, to thus uniformly extract its heat content. One such construction comprises a plurality of parallel spaced flat coils, each in the form of an Archimedean spiral, the inner end of one spiral connecting with the outer end of an adjacent spiral. To reduce the overall length and pressure drop through the coil, a plurality of coils in parallel relation may be provided, feed water being delivered to a common inlet and steam being delivered to a common outlet. A pressure equalizing tube 40 is provided, one end of which terminates in the space above the salt bed 22, the other end communicating with ambient sea water, such as the water which floods the inside of the vehicle. A valve 42 connects with the feed water conduit 44 and a like valve 46 connects with the steam delivery conduit 48.

In the operation of the vehicle and its boiler, it will be assumed that the vehicle is at the surface of the water or on the deck of surface vessel 12 and that the salt bed 22 is solidified. Suitable conduits are connected to valves 42, 46, which are connected to a recirculating source of superheated steam which is available on the surface ship. The steam is passed through coil 20 for a salt bed and as the water rises steam is formed which enters the space above the salt bed. As will be apparent, the pressure of the steam above the salt bed will balance the ambient pressure on the outside of the salt container at all depths, and, since the salt bed is now liquified it will also be at ambient sea pressure. There is thus no tendency to collapse the thin wall salt container. The vehicle continues to be propelled by the heat content of the salt bed for the desired interval, extracting the heat of the liquid salt above its solidifying temperature, its latent heat of solidification and the heat of the solid salt to a desired temperature below the temperature of solidification.

The boiler should be maintained in substantially upright position, as illustrated, and the feed water should enter at the lower end of the coil, emerging as steam from the upper end. With such arrangement, the salt bed will begin to solidify at the bottom, continuing to solidify in successive layers upwardly. The voids in any solidifying layer will be filled by the pressurized liquid salt above it and, upon complete solidification of a layer it becomes a rigid mass supporting the container against collapse.

It is thus apparent that the rate of heat transfer from the bed to the feed water and steam is greater at a lower portion of the bed than at an upper portion, thus effecting continuous upward solidification of the bed, any portion above the solidified portion remaining liquid, until finally the top liquid portion also solidifies. Since the top and last liquid portion is still at a relatively high temperature, high temperature steam can be generated throughout the entire solidification process of the bed.

An important feature of the invention is to prevent increase of volume of the salt bed when it changes from liquid to solid. Expansion, for example, would stress the container in tension tending to rupture it. Also, but less important, an undesired crushing force would be applied to the steam coil. The preferred salt bed material comprises a mixture of 60 to 90% LiOH and 40% to LiF by weight which is non-reactive with water or air. About 80% LiOl-I and LiF is ideal, providing a mixture with substantially zero coefficient of expansion during solidification. The melting point of such mixture ranges between 7508 10F thus permitting the use of superheated steam for recharging. Another mixture having similar freezing characteristics comprises about 50% of UP and 50% of BeF by weight.

The steam pressure in the coil may be as desired. If such pressure is the same as ambient pressure there will be no stress in the coil. If greater than ambient pressure it must be designed to withstand rupture in tension and if less it must be designed to withstand rupture or collapse in compression.

In instances where the boiler may be tipped from a vertical position there is a possibility of molten salt entering the top of tube 40 and solidifying in the tube. To

obviate this possibility the top of the salt bed may be isolated from tube 40 by the provision of a piston, bellows or diaphragm extending across container 18. Thus, the salt will be contained in a chamber below the top end of tube 40, and tube 40 will communicate with an adjacent chamber, pressure in tube 40 being transmitted to the salt bed through the separating wall formed by the piston, bellows, or diaphragm Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is: 1. An underwater vehicle including apparatus for generating steam for propelling same, comprising;

a. a closed thin wall container having a void space at its upper end, a meltable salt mixture filling said container below said space, said mixture having substantially zero coefficient of expansion at its solidifying temperature, the solidifying temperature being in excess of 212F, the outside of said container being in contact with and subjected to water at ambient pressure, means for pressurizing said'space to ambient water pressure whereby the salt mixture, when melted,

subjects the inside of said container to ambient water pressure,

. a steam generating coil disposed within said salt mixture having a water inlet at its lower end and a steam outlet at its upper end adapted to extract heat from the salt mixture and cause it to solidify, first at the bottom of the container, and thereafter in succeeding layers thereabove, and

f. a source of superheated steam for melting said salt mixture disposed at the surface of the water and means for connecting said coil to same.

2. Apparatus in accordance with claim 1, including porous heat insulation surrounding said container, and means surrounding the heat insulation for preventing sea water from penetrating the insulation.

3. Apparatus in accordance with claim -1 wherein said means for pressurizing said space comprises a conduit having one end communicating with ambient water and its other end communicating with said space, 

1. AN UNDERWATER VEHICLE INCLUDING APPARATUS FOR GENERATING STEAM FOR PROPELLING SAME, COMPRISING; A. A CLOSED THIN WALL CONTAINER HAVING A VOID SPACE AT ITS UPPER END, B. A MELTABLE SALT MIXTURE FILLING SAID CONTAINER BELOW SAID SPACE, SAID MIXTURE HAVING SUBSTANTIALLY ZERO COEFFICIENT OF EXPANSION AT ITS SOLIDIFYING TEMPERATURE, THE SOLIDIFYING TEMPERATURE BEING IN EXCESS OF 212*F, C. THE OUTSIDE OF SAID CONTAINER BEING IN CONTACT WITH AND SUBJECTED TO WATER AT AMBIENT PRESSURE, D. MEANS FOR PRESSURIZING SAID SPACE TO AMBIENT WATER PRESURE WHEREBY THE SALT MIXTURE, WHEN MELTED, SUBJECTS THE INSIDE OF SAID CONTAINER TO AMBIENT WATER PRESSURE, E. A STEAM GENERATING COIL DISPOSED WITHIN SAID MIXTURE HAVING A WATER INLET AT ITS LOWER END AND A STEAM OUTLET AT ITS UPPER END ADAPTED TO EXTRACT HEAT FROM THE SALT MIXTURE AND CAUSE IT TO SOLIDIFY, FIRST AT THE BOTTOM OF THE CONTAINER, AND THEREAFTER IN SUCCEEDING LAYERS THEREABOVE, AND F. A SOURCE OF SUPERHEATED STEAM FOR MELTING SAID SALT MIXTURE DISPOSED AT THE SURFACE OF THE WATER AND MEANS FOR CONNECTING SAID COIL TO SAME.
 2. Apparatus in accordance with claim 1, including porous heat insulation surrounding said container, and means surrounding the heat insulation for preventing sea water from penetrating the insulation.
 3. Apparatus in accordance with claim 1 wherein said means for pressurizing said space comprises a conduit having one end communicating with ambient water and its other end communicating with said space, an intermediate portion being in heat exchange relation with said salt mixture and adapted to generate steam from ambient water for pressurizing said space to ambient water pressure.
 4. Apparatus in accordance with claim 3 including a flexible wall within said space, one side of said wall being in contact with the entire upper surface of the salt mixture, the other side being pressurized to ambient pressure through said conduit, whereby entry of the salt mixture into said tube is prevented. 